The present invention relates to a high dispersible metal oxide fine powder added in a powder material, such as a coating powder, a toner for an electronic photograph, etc., for the purpose, such as flowability improve, caking prevention, and electrostatic charge control of a powder, and its composite. Specifically, the present invention relates to a high dispersible metal oxide fine powder, which can remarkably improve standup of the electrostatic charge, a image quality, and a cleaning characteristic, by containing said metal oxide fine powder, and to a toner composite containing said powder. In addition, the toner composite of the present invention contains the powder, which is used for not only the electronic photograph but also various electrostatic pictures, such as an electrostatic recording, an electrostatic printing, etc.
A developer of the electronic photograph, etc., has comprised the toner composite, in which some external additives are added to the toner, and contained a carrier, for example, a glass bead, an iron powder, or an ferrite carrier, etc., if necessary. As the toner of the external additive, the fine powders are used, which are surface-treated on the metal oxide fine powder, such as fine silica, titania, or alumina, etc., with an organic material, and the flowability and the electrostatic charge of the toner are controlled by this external additive. Especially, the average particle size of the toner has been made fine from about 10 xcexcm to 5 xcexcm recently because of the demand of high imaging quality of the electronic photograph. However, there is a problem with this making fine powder, in which the flowability of the toner is decreased, so that is a tendency that the amount of the external additive is increased to improve the flowability of the toner. Moreover, a characteristic of the external additive has been much influenced on the electrostatic charge of the toner by increasing said amount of the additive. For example, if the additive is distributed irregularly in the toner, a high quality development characteristic can not be obtained. For this reason, the additive having good dispersibility is required.
Conventionally, as the external additives of the toner for the electronic photograph, the metal oxide fine powder treated with hydrophobic treatment is used. When the amount of the treatment reagent used is increased to stabilize the surface treatment, it becomes agglomerated the particle, so that the flowability and the dispersibility are decreased on the contrary. Therefore, the process of pulverizing the surface-treated metal oxide powder is proposed. For example, in Japanese Patent Raid Open Hei 2-42452, or Hei 8-152742, the pulverizing to use the surface-treated metal oxide fine powder by a jet mill is shown. However, this pulverizing by the jet mill has high energy cost and, moreover, the particle size after pulverizing is very fine, so that there are problems in dust and handling.
The present invention solves the conventional above-mentioned problems about the metal oxide fine powder used as the external additive of the powder material, such as the toner, etc., and provides the metal oxide fine powder, which has low pulverizing cost, good dispersibility at the time of adding to the powder material, by using the metal oxide fine powder controlled the distribution of the agglomerated particle size according to the average particle size of the powder material, such as the toner etc. Moreover, the present invention also provides the toner composite having the stable electrostatic charge and the good flowability, by containing this metal oxide fine powder.
That is, the present invention relates to the metal oxide fine powder used as the external additive of the powder material, wherein the surface of said powder is hydrophobic treated and has high dispersibility in the powder material by which the peak of the size distribution of the agglomerated particles makes lower than the level of the average particle size of the powder material. Regarding the metal oxide fine powder of the present invention, for example, it is preferable that the average first particle size is less than 300 nm (nano meter), its agglomerated particle has the peak of the particle size distribution in the range of less than 10 xcexcm (micron meter) preferably 5 xcexcm, the specific surface area by the BET method is 10-400 m2/g, the hydrophobicity is more than 30%, and the bulk density is more than 30 g/L, preferably more than 100 g/L. Moreover, the composition of the metal oxide fine powder is, for example, silica, titania, alumina, zirconia, or these composite oxides, which are hydrophobic treated on the surface with organic silicon compounds. Moreover, the powder material added the metal oxide fine powder of the present invention is, for example, the toner for the powder coating or the electronic photograph. Furthermore, the present invention also relates to the toner composite, which has high flowability by addition with such metal oxide fine powder. It is preferable that the content of the metal oxide fine powder in this toner composite is 0.01-5.0% by weight.
[I] Metal Oxide Fine Powder
The metal oxide fine powder of the present invention is the fine powder, which is silica, titania, alumina, zirconia, a composite oxide of more than two kinds of these metals, or a mixed oxide of more than two kinds of metal oxides. In addition, in the present invention, silica is also included in the metal oxide. The metal oxide fine powder of the present invention is obtained by the surface-treatment with the organic silicon compound, etc., and pulverizing. Furthermore, it is available that the surface treatment and the pulverizing are done simultaneously, before or after.
[II] Surface Treatment
The above-mentioned metal oxide fine powder is hydrophobic treated with the surface treatment reagents, such as the organic silicon compounds. As these surface treatment reagent s, for example, a silicone oil or a silane coupling reagent, such as trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, trimethylalkoxisilane, dimethylalkoxisilane, methyltrialkoxysilane, and hexamethyldisilazane, etc., an organopolysiloxane or some modified silicone oil including an organopolysiloxane are used. The kind of these silane coupling reagents is not limited, and various kinds of alkoxysilane, chlorosilane, or silazane can be used. Moreover, the kind of the organopolysiloxane is not also limited, so that a dimethyl silicone oil, a methylhydrogene silicone oil, a phenyl silicone oil, a non-reactive silicone oil, or a reactive silicone oil, can be used.
The process and conditions of the surface treatment are not limited. It is available that the conventional surface treatment process is done. For example, an uniform surface modified metal oxide fine powder is obtained by the followings. At first, predetermined amount of the silane coupling agent or the organopolysiloxane is dropped or sprayed onto the metal oxide powder to be dispersed fully with a solvent if necessary. The dispersed powder is stirred at more than 50xc2x0 C., preferably more than 100xc2x0 C., more preferably 100xc2x0 C.-400xc2x0 C. for 0.1-5 hours, preferably 1-2 hours, and then is cooled.
[III] Hydrophobicity
Regarding the surface treated metal oxide fine powder, it is preferably that the degree of hydrophobicity measured by a transparency method is more than 30%. If the hydrophobicity is less than 30%, the improvement of the moisture resistance or the electrostatic charge stability of the toner is not sufficient when it is used as the external additive of the toner. It is more preferably that the hydrophobicity is more than 60%.
[IV] Particle Size Range
The surface modified metal oxide fine powder of the present invention is used as the external additive of the powder material, wherein the peak of the particle size distribution of the agglomerated particle (the secondary particle) is less than the same level of the average particle size of the above-mentioned powder material. It is preferably that said metal oxide fine powder has less than 300 nm (nano meter) of the average primary particle size, 10-400 m2/g of the specific surface area by the BET method and the agglomerated particle has the peak of the particle size distribution at the range less than 10 xcexcm (micro meter) preferably less than 5 xcexcm. In this case, the meaning of the powder material is the powder added the metal oxide particle of the present invention, such as the toner for the electronic photograph etc. The meaning of less than the same level of the average particle size of the powder material is same or less than the average particle size of the powder material. Moreover, the meaning of having the peak of the particle size distribution is that having the maximum value in the volume distribution curve of the particle size. In addition, the meaning of the peak of less than 10 xcexcm is that the maximum value of the particle size distribution is in the range of less than 10 xcexcm. When there are multiple peaks, the meaning of the peak of less than 10 xcexcm is that the biggest maximum value of them is in the range of less than 10 xcexcm. It is more preferably that the fine metal oxide powder of this invention has the peak of the particle size distribution in the particle size range of 0.1-10 xcexcm, wherein the agglomerated particles, which are more than 55% of a whole volume, are included.
Regarding the toner for the electronic photograph, although the toner having the average particle, size of about 10 xcexcm has been used in general, it is in the tendency that, more fine toner having the average particle size of about 5 xcexcm is used for high image quality. Therefore, in the present invention, the particle size of the agglomerated particle of the metal oxide fine powder is made to have the peak of the particle size distribution at less than 10 xcexcm, preferably less than 5 xcexcm, to be fine as the same size or less than the size of the toner. By this way, the agglomerated particle of the metal oxide fine powder can exist between the toner particles, so that the caking between the toner particles is prevented to increase the flowability of the toner composite. When the distribution peak of these agglomerated particles is in the range of more than 10 xcexcm, the metal oxide particle cannot exist between the toner particles, which have smaller size than this value, so that the flowability of the toner composite cannot be improved. In addition, since the metal oxide fine powder exists in the agglomerated state in general, when the powder, in which the primary particle size is smaller than the toner particle, is used, the sufficient effect for the flowability improve can not be acquired without controlling the particle size of the agglomerated particle. Moreover, when the average particle size of the primary particle is more than 300 nm, or the specific surface area of the primary particle is smaller than 10 m2/g by the BET method, it is not preferably since the distribution peak of the agglomerated particles is easy to be in the range of more than 10 xcexcm. On the other hand, when the specific surface area is more than 400 m2/g by the BET method, it is not preferably since the caking is too strong to become the peak of the particle size distribution more than 10 xcexcm.
[V] Pulverizing/Pulverizing Process
The metal oxide fine powder hydrophobic treated on the surface is pulverized or pulverizing processed to be prepared to the above-mentioned particle size range. It is available that this pulverizing or pulverizing process is same as the conventional one. In addition, by processing to combine the pulverizing or the pulverizing process and the classification, the metal oxide fine powder having the above-mentioned particle size can be obtained efficiently. As a pulverizing machine, a mechanical pulverizing machines, such as a pin-mill, a fine-mill, a bead-mill, a ball-mill, a hummer-mill, or a chopper, etc., can be used. As the classification process, an air classification, a sieving, or a jet sieving, etc., can be used. In addition, the actual conditions for controlling to the above-mentioned particle size range are determined according to the kinds of the metal oxide materials, the conditions of the surface modification, the pulverizing equipments, or the classification equipments. Regarding the surface treated metal oxide powder, the agglomerated particles of said powder become to the agglomerates, in which said particles combine more like a net, and, furthermore, these agglomerate combine to exist as the clusters. These agglomerates or clusters are pulverized to the level of the agglomerated particle or the primary particle by the pulverizing process.
[VI] Bulk Density
Regarding the metal oxide fine powder of the present invention, it is preferably that the bulk density is more than 30 g/L, more preferably more than 100 g/L. When the bulk density is less than 30 g/L, there are problems in dust, and handling of transportation, etc. When the bulk density is more than 100 g/L, the handling is good, and the dispersibility is improved remarkably at the time of adding to the powder. Furthermore, it is easy to control the distribution peak of the particle size.
[VII] Toner Composite
The toner composite for the electronic photograph etc. of the present invention contains the above-mentioned metal oxide fine powder having the high dispersibility. By containing the metal oxide fine powder having the high dispersibility, where the particle size of the agglomerated particle is controlled as above-mentioned particle size, said metal oxide fine powder is dispersed uniformly between the toner particles, so that it is obtained that the toner composite has the high electrostatic charge stability and the excellent flowability. Although the content of the above-mentioned metal oxide fine powder in the toner composite is based on the kinds of the metal oxide and the hydrophobicity of the powder etc., it is preferably that the content is 0.01-5.0% by weight in general. When the content is less than 0.01% by weight, the effect of addition is not acquired sufficiently. On the other hand, when the addition is more than 5.0% by weight, there is no wide difference of the flowability or the electrostatic charge stability, and there may be a problem in the image quality or the cleaning.
It is available that the composition of the toner composite of the present invention is same as the conventional composition excepting the above-mentioned metal oxide fine powder. For example, as the toner, the common used toner can be used, which is made by blending coatings, and additives, with the binder resin, i.e. the thermoplastic resin. As the additives, magnetic materials, or electrostatic charge control reagents are used if necessary. Moreover, it is available that said toner is used magnetic type or non-magnetic type, negative or positive charge, and monochrome or color. In addition, it is also available that said toner can be used as the mono component system not using a career, or the two components system using a career. In addition, in the toner composite of the present invention for the electronic photograph etc., the above-mentioned metal oxide fine powder used as the external additive can be not only used individually, but also used together with the other metal oxide fine powder. For example, the above-mentioned metal oxide fine powder can be used together with the fine silica powder produced by dry-process, the fine titanium oxide powder produced by dry-process, and the fine titanium oxide powder produced by wet-process, etc., which are surface-modified by other processes.